The accuracy of any given estimation depends on:
 Historical data
 Consistency of the level of abstraction of counted elements
 Continuous improvement of the estimating process
Historical data can be gathered from existing systems if the original cost of development in terms of time
and money is known. This is achieved by counting elements in the existing system similar to the elements
to be counted in estimating the new system. The cost per element to be used in estimating the new system
is then derived by dividing the total cost of development of the reference system by the number of those
elements in the reference system. The derived cost per element is then multiplied by the number of those
elements in the specification for the new system to produce the overall estimated cost of the new system.
Other factors may also be included and weightings are adjusted based on project experience of using the model.
